A multiplicity of processes to obtain boron compounds are well known in the art, particularly boric acid, such as the colemanite and/or the howlite minerals, as well as some other minerals containing borax, among which the process described by Taylor, U.S. Pat. No. 2,746,841, granted to Borax Consolidated, Ltd. and issued on May 22, 1956, can be mentioned. In that process a mineral containing insoluble minerals and borax (Na.sub.2 B.sub.4 O.sub.7.10H.sub.2 O), together with a mother liquid obtained from the process used for dissolving borax, are introduced in a dissolving tank, and the borate solution is separated from the insoluble fraction of the mineral in order to take the clear solution to a sulfate reactor. The solution is treated with sulfuric acid so as to convert all of the sodium oxide in the solution to sodium sulfate, thus producing an acid solution containing, primarily, sodium sulfate and boric acid. The acidified solution is heated so that the concentration of sodium sulfate exceeds the solubility of normal saturation at the existing temperature in order to precipitate anhydrous sodium sulfate. The precipitate is separated from the solution and washed so that it can be sold as pure sodium sulfate. The remaining solution, saturated with sodium sulfate and containing boric acid in elevated concentrations but not reaching saturation, is cooled or is concentrated and then cooled; this increases the solubility of the sulfate and boric acid is precipitated, which is crystallized from the cooled solution. The resulting crystals are separated from the solution and the boric acid thus crystallized is obtained as a product of the process. The remaining solution, which still contains sodium sulfate and boric acid in sufficiently high amounts to produce saturation, is returned as mother liquid to the mineral dissolving tank so that the dissolution stage can take place.
Another process known for the obtainment of boric acid is that described and claimed by Dwyer in U.S. Pat. No. 3,103,412, issued Sept. 10, 1963, assigned to Tholand, Inc. In that method, minerals containing calcium borate, such as colemanite and howlite, are treated to recover useful boron compounds from said minerals. The process comprises: mixing the mineral with aqueous ammonium sulfate; heating the mixture to produce an ammonium pentaborate mud, precipitated calcium sulfate and gangue; filtering the mud to separate calcium sulfate and the gangue; cooling the filtrate in order to crystallize the ammonium pentaborate; separating the crystalline pentaborate and reacting with sulfuric acid in order to form boric acid and ammonium sulfate. Said boric acid is recovered as a reaction product, and the ammonium sulfate solution thus formed is used to treat additional amounts of mineral.
Another process to benefit colemanite to obtain boron compounds is described by Warner, Jazzcryk; Irena, Jurkiewics and Jadwiga (Inst. Chem Nieorg., Gliwics, Pol.) Przem. Chem. 1977, 56(5), 264-6(Pol), which comprise a two-stage method for the decomposition of colemanite during the production of sodium perborate. In this process the colemanite is treated with a stoichiometric amount of sodium bicarbonate and a lower amount to the stoichiometry of caustic soda in order to form sodium borate, calcium borate and water. In the second stage, the colemanite not decomposed is treated with more caustic soda in order to obtain a stoichiometric amount for the total reaction. Then the colemanite is decomposed in a hour, which represents an improvement against the 90% decomposition of an alkaline stage process, wherein three hours are required.
Still another process to obtain boric acid from colemanite is that described by Mathis, Pierre (Solvay et Cie.) German Publication No. 2,020,570, dated Nov. 12, 1970 in which boric acid is prepared through the decomposition of crude or calcined colemanite with CO.sub.2 at a pressure higher than atmospheric pressure and at moderate temperatures in the presence of water with later separation of the solid phase from the liquid phase, and crystallization of the boric acid from said liquid phase.
Another process to obtain boric acid through the decomposition of colemanite is described by Bozadzhiev, P. (Bulgarian), God Vissh Khim-Tekhnol Inst. Sofia, 1973, 21(2), 79-84 which comprises producing boric acid by decomposition of the colmanite with monocalcic phosphate and double superphospate. Decomposition percentages of 99.9% have been reported with said monocalcium phosphate and 98.1% with the superphosphate.
Another process for the decomposition of colemanite is one described by Bozadzhiev, P. (Bulgarian), God Vissh Khim-Tekhnol Inst. Sofia, 1973, 21 (2), 67-77 in which the colemanite is decomposed in the presence of an excess of phosphoric acid through the reaction of colemanite with 15% phosphoric acid, with which a practically quantitiative decomposition within 60 minutes at low temperature, or 20 minutes at a higher temperature is achieved. The velocity of decomposition is controlled by diffusion, so that a layer of the diffusion virtually consists of pure boric acid, while starting from colemanite monocalcium phosphate is formed.
Another process to obtain boric acid starting from minerals containing calcium, sodium and boron, such as ulexite, is described by Werner Janik et al in the Polish Patent No. 218,576, issued Sept. 26, 1979 appearing in German publication No. 3,029,349, issued Apr. 16, 1981. It includes the manufacture of boric acid from Peruvian ulexite by heating of said ulexite in 96% sulfuric acid in an amount sufficient to precipitate calcium sulfate, resulting in a suspension of calcium sulfate in a solution of boric acid, plus other secondary products. The calcium sulfate is separated from the solution and is then treated with ion exchange apparatus in order to obtain the boric acid by acidification, crystallization and purification.
Finally, another process is known to obtain boric acid from minerals such as Kernite. This method is described by Miroslav Novak et al in the Czechoslovakian Patent No. 184,560, dated Feb. 15, 1981. With this method, 74 to 83% of the total B.sub.2 O.sub.3 contained in the kernite mineral or in the borax is recuperated through the decomposition of such minerals with diluted nitric acid at a relatively elevated temperature and the separation of the crude boric acid from the cooled solution. The mother liquors are concentrated to produce additional boric acid and the residual liquid phase is evaporated to give a fertilizer containing sodium nitrate and boric acid.
However, all of the processes described above and others of the prior art, require that it be carried out by the use of a starting material, i.e., a mineral of a high grade or quality and of a low degree of contamination by arsenic, since otherwise, the resulting products would be contaminated by said impurities, particularly arsenic, and the minerals are not beneficiated with adequate efficiency. There are large amounts of colemanite and howlite mineral deposits of a low grade or qaulity and which are highly contaminated. Man has searched a long time for a way to exploit the stated deposits even though to date it has not been possible in view of the fact that all of the existing processes in the prior art were unable to beneficiate the stated minerals with reasonable efficiency. Therefore, for a long time, economic and efficient processes have been searched for in order to beneficiate these type of minerals of low grade and high degree of contamination.
Even though numerous investigations have been carried out in order to exploit the stated minerals, whether by the concentration or the beneficiating methods, including the elimination of arsenic, iron and sulfate in order to obtain a boric acid useful for the glass industry, the procedures that have been tried to date using this particular method have not been entirely satisfactory. Such process have included mechanical methods, such as mill, attrition, flotation, etc., as well as chemical methods, such as the process of lixiviation, extraction by solvents or calcination. But even with all the processes that have been tried up to now, it has been found that a mineral is produced which is more or less concentrated and it can be beneficiated with an average yield rate of 38 to 48% of B.sub.2 O.sub.3 and with a relatively high recuperation rate of from 68 to 75%. These processes have not been sufficiently economical to try on an industrial scale, and they are incapable of adequately eliminating the arsenic, iron and aluminum contaminants contained in the minerals.